Transconductor employing line type field controlled semiconductor



5 o. M. STUETZER 2,657,345

TRANSCONDUCTOR EMPLOYING LINE TYPE, FIELD CONTROLLED SEMICONDUCTOR Original Filed Oct. 6, 1949 INVENTOR. 077K516 5/57756 ?atented Oct. 27, 1953 our-TED STATES PATENT OFFICE 'BEANSC'ONDUQTEEEMPEOYHVGLINE 'IEYPE FEEED; GGNFBRGLEED SEMIC6NDU1T0R Ot'mar M. SthetzeuSpringi-iehflflliih Origiiral application: Gctober 6 1949, Serial Noa 119,985; new Patent No. 23618 690, dateclNovembcr 1-8, 1952, Dividedandithis application May 20,1952, Serial'No. 28-8 996" (Grantedi under Title 35,

sec. 266

invention; described hereimmay: he manna factored andmse'dshy car for: the. Government.- for governmentall purposes without payment. to-- me am" royalty thereon.

This: application is; a) division: 015' my; applica tiOIicSen. Nor, 113,985,. filed Qctoloer 119-419;, now Patent, 2,6I8i690- ISSlIfi'di November: 18* 1952-.

inventioni relates: to transconductiue: olevices ofi type employing: a semiconductor ac the" current controlling element;

In: my patent: application: Serial: No. 11-95% ,v filed Qctoherf 4 1949; there: was described: and: claimedi a. tramsconductive: devicaemploying, a semiconductor in which; the: output electrode made aipoint. contact Witrrtha semiconductor and: in Whichatheinputor control: electrode wasposi-- tinned very: 0105651103 the point contact and v servedtoicontrch thaelectrical': fieldithe neighborhood ofi the=pointcontactfl variationsrinncontrol electrod'e potential; as asigna-L voltagarproducedc ccm'esponding; variations in; output: electrode: current. The: devicehadi high. input-impedance, high; current and; power amplification; and. highefi'iciency; It had circuit: impedance values come parable: to those of a vacuum tuhe andzwithinuits power limitations could like: a vacuum: tube; beused' as i an. amplifier, detector, oscillator, volume.- controlling device, grid;- controllect rectifiem eta The device also exhibited.a-peculiarrcharacteristic in that the sign oft its mutualzconductance: was

a: function of the: controi electrode: bias voltage: This characteristic permitted itSE use as. a. phase; inverten in which a reversal: of; phase could be produced: by! shifting. the: bias: from a. value at which the mutual conductance was-cf: one sign-to a value: at. which the? mutual; conductance was of the oppositasigne.

The transconductive. device. described: in; the; present application is vsimilar to that described above in its. characteristics and: uses but is dii ferent' in that al'ine contact, rather thana point contact, is made Between the output. electrode and the semiconductor ailine contact being do! fihedL' asnar contactarea one dimensiomof which is verylarge compared; to. the other.- This: type construction is. easier, particularly for quantity. product'ion ofthe' device, and'inad'ditionresul'ts in smaller interelectrode. capacities, higher mechanical and electrical stability" and higher power Handling capacity:

It is-' accordingly the object of the invention toprovide a* transconductive' device employing av fielid: controlled. semiconductor and having many on the: characteristics of a vacuum while nonrequining: a; heated: cathode: or? an: evacuated envelope u. so. code (1952).,-

It is a further object:- oiithe invention" to pro vide"w a transconductive device of? the semicon;-- doctor type; hacingra: input impedance; high current and; power amplification and high e'fefi'ciency.

It a still further object of the invention to provide a transcon-ductive device of the semi-- conductor type in which a line contact exists the: output: electrode and; the" semicondoctor 211812 in; which a. control: electrode is pro'-- videds for: ccntroilin the electrical field in: thenei'ghhorhond otfi the." line contactr liaise another object of: the invention to cro a transcorrductivw device of the S'Gl'filGOIl type the: design: at which! lends? itself: readily: to: modem manufacturing; techniques such as: eraporationn sputteringv electroplat-- lit stilt another: object, of the: invention to provide aitransconrluctire: device-of: the: SBmiCDIir ductorf type which hasa' high degree of; mechanica'l electrical. stability;

It isazlturthen object. of: the: invention; to; de visersuitable'processesi for manufacturing; trams-'- conductive devices oi the type: describedt The specific: details the: invention will be explained: in connection with: the: accompanying; drawing; showing; an embodimentv thereof-,7. in: which? Fig 1: isaJSchematic-r diagram of a transconr ductance: device employing? linecontact be tween: the output electrode and: the.- semicon ductor;

Fig. 2 18M]; sectional: view of. Fig t 1 Fig. 3: shows-1anassembled transoonductive de visa in. accordance with the invention;

Fig..4= showsa step=inxtheiprocess-ofi making the electrode structure of Fig 1;, and.

Fig" diaasectionalview of the 00.11112165661191613- trode structurerof Fig-r L Reicrring, to- Figs. 1. and; 2- a: transconductive: deviceiin accordance. with theinventionis sh'owll andi comprisesx a semiconductor. It, contro'L electrode II and an output. electrode t2. 'llhe output electrode 12 I consists at a: very' fine: wire: which ispressed against the'semiconductor W'- by thecontrol electrode H Thecontroli clawtrode is insulated from the wire t2; by a; sheet; of insulating. materialp I23 which: should be .as: thin aslpossiblai Aidropi of. colloidalisiluer. I4 is; de-- posited on the insulating sheet and around the end of the. control; electrode to: distribute the electricalpotential of: thecontrolelectrode over the insulating memioen- A 's semiconductorf ma teria-k. n-t-ype and: p-t3tpegermaniurmv patypei silicon: and: telluriiimi are; reccmmendedi The n-type and p-type designation is in accordance with the present theory of conduction in semiconductors, the former representing conduction by free electrons and the latter representing conduction by holes due to absences of electrons in the interatomic bonds. The output electrode I2 is shown in Fig. 1 as the core of a piece of Wollaston wire. Wollaston Wire is made up of a very fine wire relatively hard metal such as platinum as the core and an outer sheath :5 of a relatively soft metal such as silver which pro tects the fine core wire and adds sufficient strength and size to make the composite strand easy to handle. The core may have a diameter of from 2 to 5 microns and is exposed by eating away the outer layer of silver with a suitable acid usually supplied by the manufacturer of the wire. While Wollaston wire is well suited for the use as the output electrode, fine wires of other metals such as tungsten may also be employed. The insulating sheet i3 may be made of any suitable thin insulating material such as thin glass, paper or plastic material such as cellophane. The control electrode should have a flat end surface of greater dimensions than the diameter of the wire forming the output electrode.

An input circuit, consisting of input terminals l6 and bias voltage source I1, is connected between the control electrode and the semiconductor. An output circuit, consisting of load impedance l8 and direct current source IQ, is connected between the output electrode and the semiconductor. Variation of the potential of control electrode II, as by the application of a signal to terminals 16, results in corresponding variations of current in the output circuit. This is believed to be due to the variation of the electric field in the semiconductor in the neighborhood of the line contact. source I!) is normally such as to send current in the high resistance or back direction of the semiconductor. For n-type germanium operation in the back direction requires that the output electrode be negative with respect to the semiconductor as shown in Fig. 1. Operation in the forward direction is also possible and results in low noise and low relaxation efiects making such operation advantageous in some high frequency applications. Forward operation is also characterized by greatly reduced power output and output impedance as compared with operation in the back direction. The input impedance of the device is extremely high and comparable to that of a vacuum tube. The device also draws no current from bias source I I which adds to its efliciency.

Figs. 3, 4 and 5 show an arrangement for obtaining a large number of parallel acting line contacts. Referring to Fig. 3 a semiconductor 49 of cylindrical form is encased in a tube 4! of insulating material such as glass or quartz. The upper end of the semiconductor and tube assembly is a plane surface perpendicular to the axis of the assembly. An electrode structure 52, the details of which are shown in Fig. 5, is placed over the end of the semiconductor 40.

Figs. 4 and 5 illustrate the procedure for making the electrode structure 42. The dimensions being dealt with are extremely small, the diameter of the cylindrical semiconductor 40 being from to l millimeter. For this reason it is not practical to draw Figs. 4 and 5 to scale, and these figures are intended to illustrate the manufacturing processes of the electrode structure The polarity of rather than the relative sizes of the parts involved. In this case it is desired to obtain on the end of the semiconductor a large number of interconnected thin and narrow strips of metal which make substantially line contact with the semiconductor and act as output electrodes, and to apply a controlling electrical field in the open areas between the contacting strips. This is accomplished by first dusting the end of the semiconductor 40 with a powder the individual particles of which are from 1 to 3 microns in diameter. Suitable materials for this purpose are titanium dioxideand tantalum dioxide. The dusting should be such that a single layer of particles is formed with the particles not quite touching each other. The proper density would be obtained by approximately 200 particles evenly distributed over the end of a semiconductor having a diameter of /2 millimeter. These particles are represented at 43 in Fig. 4, however, as already mentioned, this figure is not drawn to scale and in an actual embodiment the density of particles would be greater so that the spacing between particles would be less than the proportionate spacing shown. A ratio of particle spacing to particle diameter of 1 to 1 or less appears to give best results. After dusting, a layer of silver or antimony 44, preferably thinner than the radius of the particles is deposited over the dusted end of the semiconductor as shown in Fig. 4. By use of a suitable mask the area over which metal is deposited may be limited to an area only slightly larger than the end of the semiconductor. The mask may also contain a slot on one side so as to deposit a connecting lead 55. After metallic layer 44 has been deposited the end of the semiconductor is wiped clean of particles so that a hole is left in the layer i l at each place where there was formerly a particle, as shown at 56 in Fig. 5. The layer 54, therefore, becomes somewhat like the bottom of a coarse sieve and, if the density of particles is as prescribed above, the small strips of metal between adjacent holes will be sufficiently narrow to approach line contact conditions. The layer 44 serves the function of an output electrode making a large number of line contacts with the semiconductor.

A thin layer of insulating material 41, Fig. 5, is next formed over the perforated disk 44. This may be accomplished by dipping the end of the device into a thin solution of a suitable nonporous insulating material such as shellac, lacquer or enamel. The solution should be sufiiciently thin that the resulting layer of insulation has a thickness of no more than 1 to 3 microns. Again a mask may be used to limit the insulation to an area only slightly larger than disc :3 After this operation a layer of metal 48, to act as a control electrode, is formed over insulation 37. This electrode may be formed by the evaporation of silver or antimony as in the case of electrode 65. A mask may be used to limit the size of the control electrode to slightly less than that of the disc of insulation 41 and to form a connecting lead $9.

The transconductive device thus formed may be connected in suitable input and output circuits asshown in Fig. 3, the circuits being the same as for Fig. 1. The control electrode acts through the holes in the output electrode to control the electrical field in the neighborhood of the line contacts between the output electrode 44 and the semiconductor, as in the case of Fig. 1.

I claim:

1. A transconductive device comprising a semiconductor, an output electrode consisting of a thin layer of metal in contact with the surface of said semiconductor, a plurality of closely spaced perforations in said layer of metal, a thin layer of dielectric material of uniform thickness extending over and in contact with said layer of metal and those areas of the semiconductor exposed by said perforations, and an input electrode composed of a layer of metal placed over and in contact with said layer of dielectric material.

2. The process of manufacturing a transconductive device of the type employing a semiconductor as the current controlling element comprising dusting the surface of said semiconductor with a powder composed of small particles to produce a single layer of mutually spaced particles. depositing a thin layer of metal over the dusted surface of said semiconductor, removing said particles from the surface of said semiconductor so as to leave holes in the deposited layer of metal, depositing a thin layer of dielectric material of uniform thickness over said layer of metal and the areas of semiconductor exposed by said holes, and depositing a second layer of metal over said layer of dielectric material.

03. The process claimed in claim 2 in which said particles have diameters of from 1 to 3 microns and in which the ratio of particle spacing to-particle diameter after the dusting process does not exceed unity.

'4. The process claimed in claim 2 in which said layers of metal are deposited by condensation from a metallic vapor.

OTMAR M. STUETZER.

References Cited in the file of this patent V UNITED STATES PATENTS bfumber Name Date 2,561,123 Kurshan July 17, 1951 2;5 95,052 Casellini Apr. 29, 1952 2,618,690 Stuetzer Nov. 18, 1952 f FOREIGN PATENTS Number Country Date 500,342 Great Britain Feb. '1, 1939 

1. A TRANSCONDUCTIVE DEVICE COMPRISING A SEMICONDUCTOR, AN OUTPUT ELECTRODE CONSISTING OF A 